Scout,
The Watchtower NWT Bible uses has been preached, which is present perfect progressive tense. They likely selected this tense to get around the notion that the preaching work was completed, but rather to suggest to Jehovah's Witnesses that the preaching work progressively continues from the past to our current present.
The Roman Catholic Douay Bible says: "If so ye continue in the faith, grounded and settled, and immoveable from the hope of the gospel which you have heard, which is preached in all the creation that is under heaven, whereof I Paul am made a minister." The Catholic translation uses the present tense as it would have been been at the time of Paul as a work that was being done at the time, with no definite end point yet.
The King James Version (KJV) states: "If ye continue in the faith grounded and settled, and be not moved away from the hope of the gospel, which ye have heard, and which was preached to every creature which is under heaven; whereof I Paul am made a minister." The King James uses the past tense.
The Orthodox New Testament (ONT) says: "if indeed you continue abiding in the faith, firmly founded and steadfast, and not moved away from the hope of the Gospel which you heard, and which was proclaimed in all the creation which is under heaven, of which I, Paul, became a minister."
The KJV and ONT Bibles use was preached or proclaimed in the past perfect tense to suggest that the preaching work is considered to be completed by the time of Paul's writing to the Colossians.
Essentially, the Catholic Douay, King James and Orthodox agree in their translation. Obviously, the Watchtower NWT is written to support their position that Christians continue to be preachers. It is the only was that the NWT translation committee (Fred Franz) could in any way attempt to promote this notion, while adhering losely to the original text that is intended to be in the past tense.
However, your question really goes to the larger concept of whether Paul considered the preaching work to have reached all creation. Paul, like many people in those days, did not know how large the planet is. Thier concept of the world was centered mostly on the far reaches of the Roman Empire, which stretched from as far north as England and Germany, south to North Africa, east from Judea to Spain in the west. This area roughly equals the size of the United States. To them, this was a huge feat considering that they either walked or took ships across the Mediterranean. By Paul's day, the Gospel had been preached all over the Roman Empire, as well as Egypt, Babylon and into India and possibly China. Paul likely could not comprehend where else the Gospel could go.
Obviously, Christians since the time of Paul considered it necessary to keep on preaching or proclaiming the Gospel as new territories and continients were discovered. I recall in the 1970s, just before the big 1975 Armageddon date, that the Watchtower Society claimsed that they had reached the entire world with the Good News as they interpret it. Of course, they backed off from this when Armageddon failed to take place.
Jim W.